To reduce noise of an electric motor, a rotor obtained by stacking a plurality of electromagnetic steel sheets with a slit is used. In the electric motor, as the amount of magnetic flux generated from a stator (magnetic flux toward the rotor) increases, the amount of magnetic flux from permanent magnets disposed in the rotor decreases. This phenomenon is generally called demagnetization (hereinafter referred to as “degradation of a demagnetization characteristic”). When the amount of magnetic flux from the permanent magnets decreases because of demagnetization, efficiency of the electric motor decreases. In view of this, to suppress demagnetization together with noise reduction, a rotor in which a tilt of a slit in the electromagnetic steel sheet is adjusted has been proposed (see, for example, Patent Reference 1).